soc: qcom: Return failure when subsystem descriptor is NULL

The check in this case was returning failure only in case of
acknowledgment gpio not being defined. Return failure also
when subsystem descriptor is NULL.

This issue was reported by static code analysis tool.

Change-Id: Iaacf11c299b8cd7f9417d3d8a67c0a6a92fcfbc6
Signed-off-by: Avaneesh Kumar Dwivedi <akdwived@codeaurora.org>